1. Field of the Invention
This invention relates to an apparatus and a method for displaying waveforms of an input signal provided to a measuring device such as an oscilloscope. More particularly, the invention relates to an apparatus and a method capable of simultaneously displaying two different time-scale waveforms of an input video signal on the same screen.
2. Prior Art
In a conventional video signal display apparatus, two waveforms in different time-scales of a video signal are selectively switched to be displayed on a screen. For example, a waveform in a frame of a video signal (a frame waveform) is displayed as shown in FIG. 1(A) in a frame waveform display mode and a waveform in a horizontal line of the video signal (a line waveform) is displayed as shown in FIG. 1(B) in a line waveform display mode, thereby one of the frame and line waveforms is selected and displayed on the screen.
In the above prior apparatus, the display mode switching operation is necessary since it is impossible for two different time-scale waveforms such as the line waveform and frame waveform to be simultaneously displayed on the same screen. Moreover, whenever a display mode switching operation takes place, the operator has to remember the previously displayed waveform in order to compare the current and previous waveforms. Thus, if the operator has difficulty in remembering the previous waveform, he/she has to switch the displayed waveform to the previous one to confirm it. Therefore, the prior apparatus has the disadvantage where when two different time-scale waveforms should be compared the operation is complicated and the operator is required to remember the once displayed waveform.
In a conventional oscilloscope, a detailed portion of the entire waveform on the display can be enlarged to be displayed by adopting a delay sweep mode, thereby enabling the entire waveform and partial waveform to be displayed on the same screen, or alternatively, these waveforms are displayed on two divided portions of the screen. In case of the oscilloscope, it is possible to display two different time-scale waveforms on the same screen by employing the delay sweep mode. However, it is still necessary to perform a fast sweep operation so as to enlarge the detailed portion in the delay sweep mode. And if the fast sweep operation is conducted, the brightness of the screen decreases since the sweep time period is shortened.